1. Field of the Invention
This invention pertains to control circuits for air conditioners, and in particular to a temperature responsive control circuit which separately controls the energization of the compressor and fan in such an apparatus.
2. Description of the Prior Art
It has been recognized for some time that the energy consumed by an air conditioning apparatus, such as a room air conditioner, can be reduced if the evaporator fan is cycled on and off concurrently with the compressor. It has also been recognized that such concurrent cycling of the evaporator fan and compressor generally causes greater fluctuation in the room air temperature maintained by the air conditioner. This is due to the fact that air conditioners are commonly provided with a single temperature sensing device, which device is often located adjacent or in thermal association with the evaporator. When such a device is used to control both the fan and the compressor, poor temperature sensing results during periods when the fan is off because room air is no longer circulated over the sensing device and, because of its proximity to the evaporator, the temperature sensed by the device is likely to be considerably lower than the actual temperature of the room air.
U.S. Pat. No. 3,635,044, issued to G. A. Heth and assigned to the assignee of the present invention, discloses the use of a separate timer motor and switch which periodically energize the evaporator fan during periods when the fan and compressor are cycled off, thereby causing room air to flow over the temperature sensing device.
U.S. Pat. No. 3,373,577, issued to R. H. Bohman, discloses an air conditioner control in which a single thermostatic device sequentially operates a pair of switches such that the fan motor is de-energized and energized at a temperature below that at which the compressor is de-energized and energized. This arrangement will cause room air to be circulated over the thermostatic device prior to energization of the compressor, but only when the sensed temperature of the sensing device reaches a predetermined level. Since the single temperature sensing device used is in thermal association with the evaporator, the sensed temperature will not correspond closely with the room air temperature until such time as the fan is energized. Thus, even though the fan is energized at a sensed temperature below that required to energize the compressor, the temperature sensed with the fan off is not truly indicative of the room air temperature. Accordingly, greater fluctuations in room air temperature will occur than would be experienced if the fan were operated continuously.
U.S. Pat. No. 3,070,972, issued to L. W. Atchison, discloses an air conditioner control in which a single temperature responsive device operates two sets of switch contacts such that the evaporator fan is switched to a low speed operation when the compressor is switched off. Such an arrangement should provide good temperature sensing of the room air but does not minimize the noise or power consumption of the air conditioner unit, as is the case with the present invention.
U.S. Pat. No. 2,044,538, issued to M. F. May, discloses a control for a central heating and cooling system which includes two thermostatic devices operating at different temperatures to control different components within the air conditioning system.